1. Field of the Invention
The present invention relates to an operation prohibiting apparatus for use in construction equipment, such as a power shovel.
2. Description of the Prior Art
A known operation prohibiting apparatus, for example a cutoff bar, is generally placed at an operator entryway of an operator cab of such a construction equipment, such as a power shovel. A known operation prohibiting apparatus will be described hereinbelow with reference to FIG. 7. An operator cab 1 is equipped with an entryway 2 open at one side of the machine body, so that the operator can get in and out of the construction equipment therethrough. An operating box 4 is disposed at the front and side of an operator's seat 3 and is provided with an operating lever 5 for operating cylinders (not shown) for driving booms and arms. Where the operating lever 5 is operated in error when the operator gets in and out of the operator's seat 3, any one of the cylinders can work accidentally. In addition, even where the engine is not in operation, if the operating lever 5 is operated by mistake when the booms or the arms are in a lifted condition, the bucket, together with the booms and the arms, can move accidentally.
For these reasons, in the prior art construction equipment, a cutoff bar 6 is designed to protrude across the entryway to the operator's seat in a first position and to be returnable to a non-protruding, second position. The cutoff bar 6 is operationally linked with a locking mechanism for a hydraulic valve for driving the cylinders so that an operating mechanism for the cylinders is unlocked when the cutoff bar 6 is in the first, protruding position.
A problem arises with such a prior art cutoff bar that it is difficult to lift the cutoff bar. The cutoff bar rotates between a generally vertical position and a generally horizontal position, and is moved manually to the generally horizontal position to gate the entryway and to the generally vertical position to allow passing of the operator into the cab. Also, the operated angular range of the cutoff bar needs to be a rotational range (stroke) of approximately 90 degrees. Accordingly, the prior art cutoff bar is difficult to raise.
Moreover, since a pivot shaft of the cutoff bar is situated under the operator cab 1, the operation of the cutoff bar requires the operator to bend forward reducing its controllability. Furthermore, since the cutoff bar is placed within the space between the operating box 4 and an inner wall of the operator cab, a further problem arises in that the effective space within the operator cab is reduced.